

contour {base}                               R Documentation

_D_i_s_p_l_a_y _C_o_n_t_o_u_r_s

_D_e_s_c_r_i_p_t_i_o_n_:

     Draws contour lines for the desired levels.  There is
     currently no documentation about the algorithm.  The
     source code is in `$R_HOME/src/main/plot.c'.

_U_s_a_g_e_:

     contour(x = seq(0, 1, len = nrow(z)), y = seq(0, 1, len = ncol(z)),
             z,
             nlevels = 10, levels = pretty(zlim, nlevels),
             xlim = range(x, finite = TRUE),
             ylim = range(y, finite = TRUE),
             zlim = range(z, finite = TRUE),
             labcex = 0,
             col = par("fg"), lty = par("lty"), add = FALSE, ...)

_A_r_g_u_m_e_n_t_s_:

     x,y: locations of grid lines at which the values in `z'
          are measured.  These must be in ascending order.
          By default, equally spaced values from 0 to 1 are
          used.  If `x' is a `list', its components `x$x'
          and `x$y' are used for `x' and `y', respectively.
          If the list has component `z' this is used for
          `z'.

       z: a matrix containing the values to be plotted
          (`NA's are allowed).  Note that `x' can be used
          instead of `z' for convenience.

 nlevels: number of contour levels desired iff `levels' is
          not supplied.

  levels: numeric vector of levels at which to draw contour
          lines.

  labcex: `cex' for contour labelling. (not yet used)

xlim, ylim, zlim: x-, y- and z-limits for the plot

     col: color for the lines drawn

     lty: line type for the lines drawn

     add: logical. If `TRUE', add to a current plot.

     ...: additional graphical parameters (see `par') and
          the arguments to `title' may also be supplied.

_S_e_e _A_l_s_o_:

     `filled.contour' for ``color-filled'' contours, `image'
     and the graphics demo which can be invoked as
     `demo(graphics)'.

_E_x_a_m_p_l_e_s_:

     x <- -6:16
     op <- par(mfrow = c(2, 2))
     contour(outer(x, x))
     z <- outer(x, sqrt(abs(x)), FUN = "/")
     ## Should not be necessary:
     z[!is.finite(z)] <- NA
     image(x, x, z)
     contour(x, x, z, col = "pink", add = TRUE)
     contour(x, x, z, ylim = c(1, 6))
     contour(x, x, z, ylim = c(-6, 6), nlev = 20, lty = 2)
     par(op)

     ## Persian Rug Art:
     x <- y <- seq(-4*pi, 4*pi, len = 27)
     r <- sqrt(outer(x^2, y^2, "+"))
     opar <- par(mfrow = c(2, 2), mar = rep(0, 4))
     for(f in pi^(0:3)) contour(cos(r^2)*exp(-r/f))

     data("volcano")
     rx <- range(x <- 10*1:nrow(volcano))
     ry <- range(y <- 10*1:ncol(volcano))
     ry <- ry + c(-1,1) * (diff(rx) - diff(ry))/2
     tcol <- terrain.colors(12)
     par(opar); par(mfrow=c(1,1)); opar <- par(pty = "s", bg = "lightcyan")
     plot(x = 0, y = 0,type = "n", xlim = rx, ylim = ry, xlab = "", ylab = "")
     u <- par("usr")
     rect(u[1], u[3], u[2], u[4], col = tcol[8], border = "red")
     contour(x, y, volcano, col = tcol[2], lty = "solid", add = TRUE)
     title("A Topographic Map of Maunga Whau", font = 4)
     abline(h = 200*0:4, v = 200*0:4, col = "lightgray", lty = 2, lwd = 0.1)
     par(opar)

